Wataru Seken wa Baka bakari

In middle school, Watabe Fuyuhiko was a top student in grades and sports, and he was looking forward to a glorious high school life. Unfortunately, three idiots stand in his way. Morino Koharu is obsessed with studying, and surpasses Watabe in academics, but she's utterly clueless about everything else. Saotome Akira is constantly exercising, and surpasses Watabe in sports, but her self-worth is tied up with her skill in sports. Izumi Chinatsu, on the other hand, is an all-around failure that simply gets in Watabe's way. Watabe interacts with Morino and Saotome to learn their secrets, and ends up paired with Izumi against his wishes. The three girls are all lonely and friendless, and interpret his interactions as friendly overtures. It looks like Watabe's school life is going to be very different than he imagined!

(Source: MangaHelpers)